Ink-jet imaging processes with an aqueous latex ink composition on offset media by using a media pre-treatment liquid in order to enhance image quality is known from the prior art.
Published US patent application No. 2011/0234690 discloses an aqueous pigmented ink composition, a treatment liquid comprising an aggregating agent that is capable of fixating the ink composition on the recording medium, which may be an offset recording medium, and a printing process comprising a treatment liquid application step and a printing step, which may be performed before or after the treatment liquid application step. The ink composition may comprise resin particles having a function of aggregating themselves of making the dispersing state thereof unstable and increasing ink viscosity so as to fix an ink composition, that is, an image, when the resin particles contact the aforementioned treatment liquid or a region onto which the treatment liquid has been applied and dried.
Published international patent application WO2013/122601 discloses an ink set comprising an ink, a treatment fluid and a fixer fluid. The ink composition may comprise latex particles, provided there are no metal salts present in the liquid vehicle of the ink composition. The fixer fluid can include a precipitating agent, for example a metal salt of a polyvalent metal cation.
Published European Patent application EP1577342 discloses an ink-jet ink configured to be printed on offset media. The ink composition comprises a pigment and a liquid vehicle that may comprise latex particulates. A fixer fluid comprising a crashing agent that can facilitate the desolubilization or precipitation of one or more component(s) of the ink-jet ink. The crashing agent may be a multivalent ion or ionic group,
A disadvantage of the known latex ink compositions that are used in combination with the known treatment liquids to print on offset media (also termed machine coated (MC) media) is that prints created in this way have poor (transport) robustness (e.g. a low rubbing resistance, a low smudge resistance, a low smear resistance). In the context of the present invention, the word robustness will be used, which includes, but is not limited to, the above disclosed wordings.
It is therefore an object of the present invention to provide an ink composition, an ink set and a printing process wherein the (transport) robustness of the printed images is improved in particular on offset media, while maintaining the print quality.